1. Field of the Invention
The present invention relates to polyamide compositions. More particularly, the invention relates to oxygen barrier polyamide compositions exhibiting high oxygen scavenging capability as well as good coinjection stretch blow moldability with polyethylene terephthalate (PET), to enable the fabrication of clear, high barrier multilayer PET bottles for long shelf-life packaging applications. Such containers are useful for packaging a variety of oxygen-sensitive food and beverage products such as beer, juices and condiments as well as certain pharmaceutical and health care products.
2. Description of the Related Art
It is well known in the art to provide polyamide based packaging articles such as films, bottles, containers, and the like, which are useful for food packaging. Many such articles are made of multiple layers of different plastics in order to achieve the desired barrier properties. For example, U.S. Pat. Nos. 5,055,355 and 5,547,765 teach laminates of polyamides and ethylene vinyl alcohol copolymers which have good oxygen barrier properties.
In order to enhance freshness preservation, it is a standard practice to package food and beverage products within a packaging structure composed of laminated sheets of two or more plastics. Such packaging structures generally include a barrier plastic layer which has a low permeability to oxygen. The packaging structure can be thin, in which case it is wrapped around the item being packaged, or it can be thick enough to form a shaped container body such as a bottle.
It is known in the art to include an oxygen scavenger in the packaging structure. An oxygen scavenger reacts with oxygen that is trapped in the package or that permeates from outside of the package. This is described, for example, in U.S. Pat. Nos. 4,536,409 and 4,702,966. U.S. Pat. No. 4,536,409 describes cylindrical containers formed from such packaging plastics.
Various types of oxygen scavengers have been proposed for this purpose. U.S. Pat. No. 4,536,409 recommends potassium sulfite as an oxygen scavenger. U.S. Pat. No. 5,211,875 discloses the use of unsaturated hydrocarbons as oxygen scavengers in packaging films. It is known in the art that ascorbic acid derivatives as well as sulfites, bisulfites, phenolics, and the like can be oxidized by molecular oxygen, and can thus serve as an oxygen scavenging material. U.S. Pat. No. 5,075,362 discloses the use of ascorbate compounds in containers as oxygen scavengers. U.S. Pat. Nos. 5,202,052 and 5,364,555 describe polymeric material carriers containing oxygen scavenging material. These polymeric carriers for the oxygen scavenging material include polyolefins, polyvinylchloride (PVC), polyurethanes, ethylene vinyl acetate (EVA) and polyethylene terephthalate (PET).
U.S. Pat. Nos. 5,021,515, 5,049,624 and 5,639,815 disclose packaging materials and processes therefor which utilize a polymer composition which is capable of scavenging oxygen. Such compositions include an oxidizable organic polymer component, preferably a polyamides such as nylon MXD6, and a metal oxidation promoter, such as a cobalt compound. These compositions can be used with PET, for example.
U.S. Pat. No. 5,529,833 describes the use of a composition comprising an ethylenically unsaturated hydrocarbon oxygen scavenger which is incorporated into a film layer, and used for making packaging for oxygen sensitive products. The oxygen scavenger is catalyzed by a transition metal catalyst and a chloride, acetate, stearate, palmitate, 2-ethylhexanoate, neodecanoate or naphthenate counterion. Preferred metal salts are selected from cobalt (II) 2-ethylhexanoate and cobalt (II) neodecanoate. Because water deactivates the oxygen scavenger composition, the composition can only be used for packaging for dry materials.
Despite these advances in the art, there still remains a need for a barrier polymer material which can provide high oxygen scavenging capability in order to reduce the oxygen permeation into a container. There also is a particular need for oxygen scavenging polymeric materials which meet the processing requirements for coinjection molding and reheat stretch blow molding with PET to permit the fabrication of transparent multilayer barrier PET bottles. For the latter requirement, the material must be (a) melt processable at high temperatures of up to 280xc2x0 C. without degradation, (b) slow to crystallize, like PET, during injection molding such that the molded preform is sufficiently amorphous to permit subsequent reheat, stretch-blow molding into an oriented bottle and (c) low in crystallinity to give a barrier layer with high clarity and delamination-resistance (good adhesion) to PET layer.
The invention provides a polyamide composition which comprises:
a) a slow crystallizing polyamide blend comprising (i) an amorphous, semiaromatic polyamide homopolymer, copolymer or mixture thereof and (ii) a semicrystalline, aliphatic polyamide homopolymer, copolymer or mixture thereof wherein in the weight ratio of (i):(ii) ranges from about 99:1 to about 30:70;
b) at least one polyamide-compatible, oxidizable polydiene; and
c) at least one oxidation promoting metal salt catalyst.
The invention further provides an oxygen barrier film comprising a layer of a polyamide composition which comprises:
a) a slow crystallizing polyamide blend comprising (i) an amorphous, semiaromatic polyamide homopolymer, copolymer or mixture thereof and (ii) a semicrystalline, aliphatic polyamide homopolymer, copolymer or mixture thereof wherein in the weight ratio of (i):(ii) ranges from about 99:1 to about 30:70;
b) at least one polyamide-compatible, oxidizable polydiene; and
c) at least one oxidation promoting metal salt catalyst.
The invention still further provides a multilayer article which comprises:
a) a polyamide composition layer comprising a slow crystallizing polyamide blend comprising (i) an amorphous, semiaromatic polyamide homopolymer, copolymer or mixture thereof and (ii) a semicrystalline, aliphatic polyamide homopolymer, copolymer or mixture thereof wherein in the weight ratio of (i):(ii) ranges from about 99:1 to about 30:70; at least one polyamide-compatible, oxidizable polydiene; and at least one oxidation promoting metal salt catalyst; and
b) a thermoplastic polymer layer on one or both sides of the polyamide composition layer.
The invention still further provides a shaped article which comprises a polyamide composition comprising:
a) a slow crystallizing polyamide blend comprising (i) an amorphous, semiaromatic polyamide homopolymer, copolymer or mixture thereof and (ii) a semicrystalline, aliphatic polyamide homopolymer, copolymer or mixture thereof wherein in the weight ratio of (i):(ii) ranges from about 99:1 to about 30:70;
b) at least one polyamide-compatible, oxidizable polydiene; and
c) at least one oxidation promoting metal salt catalyst.
The invention still further provides a process for producing a polyamide composition which comprises:
a) melting a slow crystallizing polyamide blend comprising (i) an amorphous, semiaromatic polyamide homopolymer, copolymer or mixture thereof and (ii) a semicrystalline, aliphatic polyamide homopolymer, copolymer or mixture thereof wherein in the weight ratio of (i):(ii) ranges from about 99:1 to about 30:70;
b) blending the molten polyamide blend with at least one polyamide-compatible, oxidizable polydiene and at least one oxidation promoting metal salt catalyst to thereby form a mixture; and
c) cooling the mixture.
The invention still further provides a process for producing an oxygen barrier film which comprises:
a) melting a slow crystallizing polyamide blend comprising (i) an amorphous, semiaromatic polyamide homopolymer, copolymer or mixture thereof and (ii) a semicrystalline, aliphatic polyamide homopolymer, copolymer or mixture thereof wherein in the weight ratio of (i):(ii) ranges from about 99:1 to about 30:70;
b) blending the molten polyamide blend with at least one polyamide-compatible, oxidizable polydiene and at least one oxidation promoting metal salt catalyst to thereby form a mixture;
c) extruding, casting or blowing the mixture into a film; and
d) cooling the film.
The invention still further provides a process for producing an oxygen barrier polyamide film which comprises:
a) melting a composition which comprises a slow crystallizing polyamide blend comprising (i) an amorphous, semiaromatic polyamide homopolymer, copolymer or mixture thereof and (ii) a semicrystalline, aliphatic polyamide homopolymer, copolymer or mixture thereof wherein in the weight ratio of (i):(ii) ranges from about 99:1 to about 30:70; at least one polyamide-compatible, oxidizable polydiene; and at least one oxidation promoting metal salt catalyst;
b) extruding, casting or blowing the composition into a film; and
c) cooling the film.
The invention still further provides a process for producing a multilayer article which comprises:
a) melting a slow crystallizing polyamide blend comprising (i) an amorphous, semiaromatic polyamide homopolymer, copolymer or mixture thereof and (ii) a semicrystalline, aliphatic polyamide homopolymer, copolymer or mixture thereof wherein in the weight ratio of (i):(ii) ranges from about 99:1 to about 30:70; at least one polyamide-compatible, oxidizable polydiene; and at least one oxidation promoting metal salt catalyst to thereby form a mixture;
b) separately melting a thermoplastic polymer composition;
c) coextruding, casting, blowing, thermoforming, blow molding or coinjecting the mixture and thermoplastic polymer composition into a multilayer article; and
d) cooling the article.
The invention still further provides a process for producing a multilayer article which comprises:
a) melting a slow crystallizing polyamide blend comprising (i) an amorphous, semiaromatic polyamide homopolymer, copolymer or mixture thereof and (ii) a semicrystalline, aliphatic polyamide homopolymer, copolymer or mixture thereof wherein in the weight ratio of (i):(ii) ranges from about 99:1 to about 30:70; at least one polyamide-compatible, oxidizable polydiene; and at least one oxidation promoting metal salt catalyst to thereby form a mixture;
b) separately melting a thermoplastic polymer composition;
c) coinjecting molding the mixture and thermoplastic polymer composition into a multilayer preform;
d) reheating the perform; and
e) blow molding the perform into a multilayer article.
The invention still further provides a multilayer article formed by a process comprising:
a) melting a slow crystallizing polyamide blend comprising (i) an amorphous, semiaromatic polyamide homopolymer, copolymer or mixture thereof and (ii) a semicrystalline, aliphatic polyamide homopolymer, copolymer or mixture thereof wherein in the weight ratio of (i):(ii) ranges from about 99:1 to about 30:70; at least one polyamide-compatible, oxidizable polydiene; and at least one oxidation promoting metal salt catalyst to thereby form a mixture;
b) separately melting a thermoplastic polymer composition;
c) coinjecting molding the mixture and thermoplastic polymer composition into a multilayer preform;
d) reheating the perform; and
e) blow molding the perform into a multilayer article.
This invention provides a barrier polymer material which can provide high oxygen scavenging capability in order to reduce the oxygen permeation into the container. This invention further provides oxygen scavenging polymeric materials which meet the processability requirements for coinjection moldability and reheat stretch blow moldability with PET to permit the fabrication of transparent multilayer barrier PET bottles. The polyamide compositions of this invention are suitable for coinjection stretch-blow molding with PET, to thereby form a multilayered film which serves as a barrier layer suitable for bottles for extended shelf-life packaging of oxygen-sensitive food and beverage products.